There's been some discussion about that on a facebook group. If you can let me know what changes you make to Free42 to make it fall in line with Emu42, I'll get the online encoder/decoder to do the same.

I made the changes and released a new version, 2.0.16, which is out now for all platforms.

It recognizes 112-116 as ST T-ST L for all HP-41 instructions; 102-111 and 123-127 as A-J and a-e for LBL, GTO, XEQ, KEY GTO, and KEY XEQ, and everything else as numeric.

It executes functions with such nonstandard parameters like the real HP-42S does, except for being a bit more lenient: LBL >= 100 can be reached indirectly, and LBL ST T can be reached by GTO ST T and GTO 112, etc.